A Beneficial Reuse of Incinerator Fly Ash Following Phosphate Treatment: Reaction Kinetics and Control of Properties by Calcination

摘要

Beneficial reuse of municipal solid waste incinerator (MSWI) fly ash is possible following the removal of soluble alkali chlorides by water washing. Heavy metal ions can be prevented from leaching by treating the washed fly ash with H_3PO_4. The transformation of available toxic metals into insoluble phosphates depends on thorough mixing of the H_3PO_4 and the fine particle aqueous suspension. Rheological study of the pastes formed helps to determine the proper conditions for industrial application. Hydroxylapatite (HA) is a typical calcium phosphate model for insoluble minerals. We show that synthetic HA has a large surface area and capacity for retention of Pb ions. Thermal treatment of HA and metal containing HA causes a decrease in specific surface area starting near 650°C. Thermomechanical studies show this is combined with shrinkage of the matrix. Thus, calcination of the H_3PO_4-treated fly ash produces a densified material that can be considered for beneficial reuse. Further research is under way to optimize the reaction conditions, minimize the treatment cost and demonstrate the nonhazardous nature of the transformed and recycled mineral species derived from fly ash.